Transfer case differential mechanism



Jan. 26, 1954 A. F. MYERS TRANSFER CASE DIFFERENTIAL MECHANISM 4 Sheeis-Sheet 1 Filed Dec. 3, 1951 Fag. 2.

INVENTOR Albert F. Myers ATTORNEY5 Jan. 26, 1954 A. F. MYERS 2,667,088

TRANSFER CASE DIFFERENTIAL MECHANISM Filed Dec. 5, 1951 4 Sheets-Sheet 2 INVENTOR 2. 6 AlbrfiEMgerS Y ,ww 9 m ATTORNEYS Jan. 26, 1954 A. F. MYERS 2,667,088

TRANSFER CASE DIFFERENTIAL MECHANISM Filed Dec. 3, 1951 4 Sheets-Sheet 5 5 & Q0 mm @W J K E r o ms W. w, Ow W Wm -n w m6 \QW m O0, m6 mm on mm mm, A w

Jan. 25, 1954 MYERS 2,667,088

TRANSFER CASE DIFFERENTIAL MECHANISM Filed Dec. 5, 1951 4 Sheets-Sheet 4 INVENTOR Albert E'Myenr Y @cmmm,7(wm m ATTORNEYS Patented Jan. 26, 1954 TRANSFER CASE DIFFERENTIAL MECHANISM Albert F. Myers, Berkley, Mich., assignor, by mesne assignments, to Patent Developers, Inc., Detroit, Mich., a corporation of Michigan Application December 3, 1951, Serial No. 259,570

22 Claims. 1

This invention relates to the driving mechanism of automotive vehicles, and is particularly directed to the provision of a new and improved differential mechanism of the automatic overrunning or declutching type for distributing driving torque between the axles of vehicles which are adapted to drive on more than one axle. Inasmuch as devices of this character are customarily installed in transfer cases or drop boxes, they will be referred to hereinafter as transfer case differentials, for convenience.

Differential mechanisms are already known which comprise a central annular driving member having clutch teeth formed on the opposite sides thereof, a pair of driven members, axially shiftable against spring pressure, having clutch teeth engageable with those of the driving member and driving connections to the axles, and cooperating cam elements associated with the driving and driven members, respectively, which repeatedly declutch and reengage either driven member when its associated axle overruns the driving member. See, for example, my Patent No. 2,329,075 and Knoblock Patent No. 2,329,059, both dated September '7, 1943. In these prior devices, the repeated meshing and demeshing of the clutch and cam teeth during overrunning gives rise to certain disadvantages which limit their utility as transfer case differentials and which it is the aim of this invention to overcome.

It has also been proposed to incorporate in these known forms of differentials additional cam rings, commonly designated as holdout rings, which move both axially with and rotatably relative to the demeshed members and function to prevent reengagement of the latter as long as the overrunning continues. Two such structures are disclosed in the copending application of Frederick D. Knoblock, Serial No. 87,280, filed April 13, 1949, now Patent #2,638,794. One of the objects of the present invention is to improve and simplify the construction and mode of operation of the devices of this Knoblock application, and to adapt them especially for transfer case use.

Another object of the invention is to provide a transfer case differential of novel, simple design which is particularly well adapted for installations wherein one side of the differential must furnish a positive drive at all times to one axle or bogie while the other side is connected to another axle or bogie which normally overruns and is positively driven only when the first one loses traction.

A further object is to provide an improved differential of the automatic overrunning type which is rugged and dependable in operation, requires a minimum of machining in its manufacture, and, by virtue of its symmetrical design, can be readily installed and serviced in the field without danger of incorrect assembly or orientation.

These and other objects will appear more fully upon consideration of the following detailed description of the embodiments of the invention which have been illustrated in the accompanying drawings. It is to be expressly understood, however, that these drawings are exemplary only and are not to be construed as defining the limits of the invention, for which latter purpose reference should be had to the appended claims.

Referring now to the drawings, wherein like reference characters indicate like parts throughout the several views:

Fig. 1 is a diagrammatic representation of the driving mechanism of one form of automotive vehicle in which the transfer case differentials of the present invention find particular utility;

Fig. 2 is a side view, partially in section, of one form of differential embodying the invention which may be used in the transfer case or drop box of the vehicle shown in Fig. 1 or in similar installations where a positive drive is required at all times to one axle or bogie while another axle or bogie may overrun;

Fig. 3 is an enlarged half axial section of the differential of Fig. 2 showing the position of the parts when the front axle of the vehicle of Fig. 1 is overrunnmg;

Fig. 4 is a face view, partially in section, of one of the driven clutch and cam members and associated holdout ring of the differential of Figs. 2 and 3;

Fig. 5 is a sectional view taken substantially on the line 5-5 of Fig. 4;

Fig. 6 is a perspective exploded view of the differential of Figs. 2 and 3 showing the principal parts thereof separated from one another, the springs and spring retainers having been omitted for greater clarity;

Fig. 7 .is a fragmentary developed edge view of the holdout rings and cam elements of the differential of Figs. 2 and 3 showing the relative positions of said rings and elements when both driven members are fully engaged with the driving member as indicated in Fig. 2;

Fig. 8 is a view similar to Fig. 7 but showing the relative positions of the parts when the axle connected to the left-hand driven member is overrunningthe driving member as in Fig. 3;

Fig. 9 is a half axial sectional view similar to Fig. 3 showing a modified form of differential embodying the invention; and

Figs. 10 and 11 are views similar to Figs. '7 and 8, respectively, showing the relative positions of the holdout ring and cam elements of the differential of Fig. 9.

There is illustrated in Fig. 1 one type of automotive vehicle wherein the transfer case differentials of the present invention are particularly."

useful, this figure representing the driving mech anism of a 4 x 4 truck having 'a front driving axle 2i and a rear driving axle 22 with an intermediate transfer case or drop 100x23 both axles being driven from the engine2il'througha the front axle 2| normally is not driven, but receives driving torque only when the wheels of the rear axle 22 lose traction. To this end, the front axle 2! is so constructed as to normally overrun the engine-driven element in the transfer case 23 which is adapted to supply driving torque to the shafts 25 and 21, and means are provided for eifecting a positive drive to the front axle only when the engine-driven element speeds up relative to the front axle sufficiently that its speed is equivalent to that of the front shaft 26, as would occur when the wheelsof the rear axle start to slip. To obtain the normal overrunning action of the front axle, its ring gear may be provided with a few more teeth than the ring gear of the rear axle, the result being that, with all wheels rolling at substantially the same speed, the front wheels drive the shaft 26 at a slightly greater velocity than the shaft 2'! is driven by the engine-driven member in transfer case 23. In order that this arrangement 7 may function properly, there must be interposed between the shaft 26 and the engine-driven member in the transfer case a device of the overrunning clutch type which will disconnect shaft 26 and the engine-driven member. aslong as, the speed of the former exceeds thatof the latter, but will form a positive driving-connection therebetween whenever the speed of the engine-driven member becomes equal to that of said'shaft.

Turning now to Figs. 2-8, therecis shown there in one form of differential mechanism embodying the present invention which is especially well adapted for use as the power output elementof transfer case 23 and which provides a positive drive at all times to shaft 21 and rear axle 22 while simultaneously functioning as an overrunning clutch between the shaft 26 leading to front axle 2| and the engine-driven gearing of the transfer case.

As shown best in Figs. 2 and 3, the differential assembly is housed in a two-part casing 28, held together by bolts 29, which casing is provided with an external gear 30 adapted to be driven from the engine 24 through the transmission 25 and appropriate gearing in the transfer case 23. The casing 28 also has a pair of horizontally projecting bosses 3i and 32 into which extend the inner ends of opposed shafts 33 and 34 which'are in turn operatively connected .to theaxledriving shafts 26 and 21, respectively, in any suitable manner, as by universal joints.

The diiferential mechanism mounted in the casing 28 comprises as its principal elements an annular center driving clutch member 35, a pair of driven combined clutch and cam members 35 and 31 located on opposite sides of the driving member 35, a pair of holdout rings 38 and mounted on the driven members it and 31', respectively, and a pair of compression springs 45 and ll and associated sprin retainers t2 and 43 which are so arranged as to yieldably urge the clutch and cam members of the assembly into engagement with one another.

In'the embodiment of the invention illustrated in Figs. 2-8, the differential mechanism within the casing 28 is symmetrical with respect to the central plane of the driving member 35 even though the right-hand driven member 3? is intended to remain in engagement with the driving member at all times while the left-hand member 36 moves axially outwardly and inwardly relative to the driving member, out of and into engagement with the latter, depending upon the relative velocities of the associated shaft 33 and the driving member. The principal advantage of making the device symmetrical is that, both sides of the differential being alike, there is no danger of installing it incorrectly in the casing as would be true were the two sides of different construction. The symmetrical design is also more economical to service since the right-hand and lefthand driven members, holdout rings, springs and spring retainers are interchangeable; in fact, in the event of wear or minor injury to the elements of the declutching left-hand side of the device, it is only necessary to remove the casing and turn the differential end-for-end in order to remedy the defect Without replacement of any parts whatever.

The center driving member 35 has a radially extending flange 44 which is clamped between the cooperating flanges 45 and Q5 of the two halves of casing 28, the bolts 29 passing through holes in flange id and fixing the driving memher to the casing for rotation therewith. The driving member 35 is also provided on each of its side faces with a set of driving clutch teeth 4 preferably slightly undercut, which are adapted to engage similar driven clutch teeth iii} formed on the-opposing side faces of the driven clutch and cam members 35 and 37. As indicated in the lower portion of Fig. 2, the spaces between adjacent teeth of each set are Wider than the clutch teeth themselves so as to facilitate disengagement of the teeth when the overrunning driven member is moved axially outwardly away from the driving member by operation of the cam elements next to be described.

In the structure illustrated, each of the driven members 35 and 3': includes a cam ring portion 49 integral therewith which extends axially inwardly through the central opening in driving member 35 and is provided at it inner edge with a plurality of cam teeth 5%, preferably equal in number to clutch teeth adapted to cooperate with similar cam teeth formed on the inner edge of the corresponding portion of the other driven member. With this construction, since it is desirable to make the two driven members duplicates of one another, and since the two sets of driving clutch teeth l! preferably lie directly opposite one another, it is necessary to offset the cam teeth Ell with respect to the driven clutch teeth 48 so that the cam teeth of the two driven members may mesh properly with one another when the clutch teeth of both driven members are in engagement with those of the driving member 35. The radial center line of each cam teeth at is therefore offset from the center line of one of the clutch teeth l8, as shown in Fig. 4, by an angle 45 equal to one-fourth of the angular spacing between adjacent teeth. For example, in a driven member of the form shown in the drawin s, wherein there are seventeen clutch teeth and seventeen cam teeth, the center lines of the latter shculd be ofiset with respect to those of the former by an angle of approximately 5 17' 33".

In order to enable outward axial movement relative to the center driving member of whichever of the driven members is associated with the normally overrunning axle so as to effect disengagement of the driving and driven clutch teeth at that side of the diiferential when overrunning occurs, both driven members are internally splined as indicated at 5! and are slidably mounted on similarly externally splined portions 52 and 53 or" shafts 33 and 34, respectively. The driven members are urged inwardly toward one another and the driving member so as to bring the clutch and cam teeth into engagement by th springs ii! and ti, one of which is adapted to yield upon overrunning to permit disengagement of the overrunning side of the difierential. In the form shown, the springs surround the driven members with their outer ends abutting against the radially cuter portions of spring retainers 42 and which in turn abut the adjacent walls of casing 23, and their inner ends thrusting against suitable seating surfaces formed on the driven members. The spring retainers are provided with radially inwardly extending flanges 54 which are notched or splined correspondingly to splines 52 and 53 of shafts 33 and 34 so as to insure that the spring retainers rotate with said shafts and the associated driven members, thereby avoiding relative rotation between the ends of the springs and the surfaces against which they abut.

As shown best in Fig. 3, the bodies and internal splines 5! of the driven members are shorter than the external splines 52 and 53 of the shafts 33 and 34 so as to leave a clearance between the outer edge of each driven member and the adjacent spring retainer flange 54 which is greater than the depth of the clutch and cam teeth and nus suiiicient to permit full disengagement of either driven member by outward axial movement thereof relative to the driving member. However, since it is intended that the clutch teeth 48 of the right-hand driven member 3? in the illustrated embodiment of the invention shall remain at all times in engagement with the righthand set of clutch teeth l! of the driving member, means are provided for positively preventing outward movement of said driven member. As one example of a suitable means for this purpose, a blocking ring 55 may be interposed as shown between the axially outer edge of driven member 37 and the flange 5d of spring retainer as, said ring surrounding and resting on the outer portions of the splines 53 on the shaft 34.

Assuming that both driven members 36 and 37 are fully en aged with the driving member 35, as indicated in Fig. 2, and that the differential mechanism is installed in the transfer case 23 of Fig. 1 with the shafts 33 and 34 of the differential drivingly connected to the shafts 26 and 21, respectively, leading to the axles 2i and 22, overrunning of the front axle 2! with respect to the rear axle will automatically produce disengagement of the driving and driven clutch teeth at the left-hand side of the differential due to the outward axial movement of driven clutch member 36 produced by the cooperative action of cam teeth of both driven members when driven member 35 begins to rotate at a greater speed than the driving member.

For example, assuming that the ring gear of the differential in front axle 2| has one or two more teeth than the ring gear of the rear axle and that the vehicle starts to move forwardly on level ground, the greater gear ratio of the front axle will cause the shafts 26 and 33 and driven member 36 to rotate at a greater velocity than driving member 35. As driven member 36 rotates ahead of the driving member, a, movement made possible by the clearance between the driving and driven clutch teeth shown in the lower portion of Fig. 2, the cam teeth at on cam portion 49 of driven member 36 begin to ride up on the inclined sides of the cooperating cam teeth 50 of driven member 3! which continues to be driven by driving member 35 at the same speed as the latter due to the positively maintained engagement of the clutch teeth at the right-hand side of the difierential. As the cam teeth of driven member 36 ride up on the teeth of driven member 31, driven member 36 is moved axially outwardly against the force of spring 40, sliding on the splined portion 52 of its associated shaft 33, until said cam teeth are fully disengaged and are riding in end-to-end relationship, at which time the left-hand set of driving and driven clutch teeth 41 and 48 are also completely disengaged and in end-to-end relationship.

Were it not for the presence of the holdout ring 38, the construction and operation of which are next to be described, continued overrunning of front axle 2! would result in repeated engagement and disengagement of the clutch and cam teeth of driven member 35 with those of the driving member and driven member 31, with the consequent disadvantages inherent in this type of operation, such as increased wear of the cam and clutch teeth, spring fatigue and noise. However, by incorporation in the difierential of holdout rings of new and simple construction, the driven member on the overrunning side of the mechanism may be readily maintained in completely disengaged position as long as the overrunning continues, and yet be automatically returned to the fully engaged position of Fig. 2' whenever the overrunning ceases.

In the embodiment of the invention represented in Figs. 2-8, the holdout rings 38 and 39 are of the form perhaps best illustrated in the exploded view of Fig. 6, and are mounted on the driven clutch and cam members in the manner indicated best in Figs. 4 and 5. As shown, each ring comprises a circumferentially solid band 5% having at one edge a radially inwardly projecting flange 51 adapted to have a sliding fit on the outer peripheral surface of the cam ring portion as of the associated driven member, and at its opposite edge a plurality of circumferentially spaced, axially extending projections in the form of stepped lugs 58 which are adapted to cooperate with the lugs of the other holdout ring in the manner hereinafter described for the purpose of maintaining the driven member on the over-running side of the differential in declutched or disengaged position as long as the overrunning continues.

Each holdout ring is maintained in position on the associated driven member by a friction spring 59: consisting of a flat strip of: spring: steel? bent into polygonal form, said spring-being interposed. between the inner surface of the band 56 of the'. holdoutring adjacent the flange-51 and the'outer:

surface of cam ring portion 49 is provided with a circumferential groove 89'' of substantially the same width as spring 59 in which lie the central portions of the straight sides of the spring when the mechanism is assembled. With this arrangement, abutment of one edge of thespringagainst flange and of the opposite'edge against the opposing wallof groove fit-locks the holdout ring against axial movement with respect to the cam ring portion of the driven member, while at the same time the holdout ringiscapa-ble of rotation relative to the driven member againstthe frictional resistance created-by the areas of contactbetween the spring, the holdout ring and. the'cam ring portion of the driven member.

In view of the fact that relative rotation; takes place between one of the holdout rings and the associated driven member when one sideof the differential overruns, it is preferableto provide a wear-resisting thrust washer 6'! between the axially outer edge of each holdout ring and adjacent portion of the inner side face of the driven member lying radially inwardly of the clutch teeth between the latter and theouter surface of ring portion 49;

In the construction illustrated, each holdout ring is provided with four symmetrically formed stepped lugs 58, each lug having a pair of steps 62 located on opposite sides of acentral portion which extends outwardly beyond the cam teeth 50. As indicated best in. Figs. 5, 'Z'and'i, the surfaces of steps 62 which are perpendicular to the axis of the differential, hereinafter called. the end surfaces for convenience, lie in a plane which is preferably located slightly beyond the plane of the ends or tops of the cam teeth 50; i. e., the steps 62 are preferably slightly higher-"than th'e' cam teeth 5-3. As will be apparent from the subsequent description, this difference in height of the steps 2 andca-m teeth 5 provides asmall axial clearance between the disengaged cam andclutch teeth when overrunning occurs and thus avoids the wear and'noise thatwouldresult were said teeth to have end-to-end contact with one another during overrunning. The'corner of each step (52 is beveled at least down to the plane of the ends of the cam teeth, as indicated'at 53, in order to insure e desired method of operation hereinafter desci Referring now particularly to Figs. 4, 7 and 8, it will be seen that each of the spaces or'recesses 6 between adjacent 58 of'each holdout rin has a circumferential or arcuate' extent'which is greater than the circumferential extent of' one of the stepped lugs, as measured between the side surfaces of the steps, and has an axial-depth which is slightly greater than the length of'the central portion of th lug. so that when both sides of the diiierential mechanism are fully engaged, the lugs on one holdout ring extend into the spaces between the lugs ofthe other ringwith surficient clearance to permit relative rotation of one holdout ring with respect to the other; In

the embodiment illustrated, wherein each'holdout ring is provided with four lugs-and each 8. driven member has seventeen cam teeth, the circumferential extent of each of the lugs, measured between the side surfaces of the steps, is equal to approximately 2 times the circumferential extent of one full cam tooth, while each of the spaces 64' has a circumferential extent approxi mately equal to that of 3 11 cam teeth. Consequently, when both sides of the differential are fully engaged as indicated in Figs. 2 and 7, the lugsof each ring are received in the spaces or recesses of the other with a total clearance between the side surfaces of the steps of each lug and the adjacent side surfaces of the steps of the lugs on both sides thereof which is approxhnately equal to the circumferential extent of one full cam tooth.

It will also be. seen from Fig. 7 that the axial dimensions of the stepped lugs 58 are so proportioned that,.when both driven members are fully engaged with the driving member, the stepped portions of the lugs of the two rings overlap one another. axially for a distance x which is at least equal to, and preferably slightly greater than, the height of the cam'teeth 56'.

The function and method of operation of the holdout rings 38 and 39 will appear most readily from a consideration of Figs. '7 and 8 of which Fig. 7 illustrates the relative positions of the holdout rings and the cam teeth of the driven members when both of said members are fully engaged with the driving member, as in Fig. 2, while Fig; 8 indicates the relative positions of the same parts when the left-hand side of the differential is overrunning, as in Fig. 3.

In the engaged condition of Fig. 7, the cam teeth 58 of both driven members are fully meshed with one-another and the stepped lugs 58 of each holdout ring project their maximum distance into the spaces 64 of the other ring. Since at this time there is no force exerted on the holdout rings, other than inertia, tending to produce relative rotation between them and their respective driven members, the holdout rings rotate with the driven members without relative movement therebetween due to the friction clutch effect of the springs 59'and float, so to speak, in the spaces 64.

If, however, as has been previously assumed, the left-hand side of the differential begins to overrun-and the driven member 36 rotates at a greater-velocity than the center driving member 35, the cam teeth 50 which are integral with driven member 36 ride up on the cam teeth of drivenmember 31 and cause the overrunning driven member tomove axially outwardly and disengage'the left-hand set of clutch teeth 41 and 58'. During the'time that the cam teeth of driven member 36 are riding up the inclined sides of the teethof member 31 and during the initial period of the ensuing end-to-end sliding contact of said teeth, the holdout ring 38 on the overrunning driven member 35 continues to move with the latter forwardly with respect to the driving member and driven member 37, including the holdout ring 39 carried by the latter, due to the frictional connection between the two elements established by the spring 59. As this forward movement continues, the advancing beveled corners 63'of the steps 62 on holdout ring 38 come into contact with and slide over the corners of the adjacent steps on holdout ring 39 and, the springs 59 still being effective to resist relative rotation between the holdout rings and their associated driven members, move driven member pletely separate the clutch and cam teeth of said member from the corresponding teeth of the driving member and driven member 37. Since the total clearance between the side surfaces of the steps of each lug and the adjacent side surfaces of the steps of the lugs on both sides thereof is substantially equal to the circumferential extent of one full cam tooth, it is evident that the beveled corners of the steps will come into contact with one another before the lefthand driven member has rotated ahead of the driving member and right-hand driven member far enough to permit remeshing of the cam teeth of the two driven members.

The forward rotational movement of holdout ring 38 relative to holdout ring 39 then continues until the advancing side surfaces of the central portions of stepped lugs 58 of ring 38 come into abutment with the side surfaces of the steps 62 on ring 39, whereupon holdout ring 38 becomes immobilised with respect to holdout ring 39 in the position shown in Fig. 8, with one step of each lug of one ring resting on one step of one of the lugs of the other ring. Thereafter the holdout ring 38 may slip frictionally with respect to the associated driven member 39 as long as the latter rotates at a greater velocity than the center driving member 35 and driven member 37. In some instances, such as when the spring 59 associated with the holdout ring 38 is stronger than the corresponding spring at the right-hand side of the mechanism, holdout ring 3 3 may continue to rotate with the overrunning driven member 36 and carry with it holdout ring 353 so that the latter slips with respect to driven member 31. In either case, however, the holdout rings move together in the position shown in Fig. 8 and effectively maintain the 1eft-hand overrunning driven member 36 in disengaged position as long as the overrunning continues. In other words, as long as the vehicle shown in Fig. 1 is driving in a normal manner with full traction on the rear wheels, the left-hand side of the difierential overruns and is maintained in disengaged or declutched position.

if, on the other hand, the elements of the drive to the rear axle 22 speed up sufficiently that the rotational velocity of driving member 35 and driven member 3? increases relative to and tends to exceed that of driven member 36 and the other elements normally driven by the overrunning front axle, a condition which would occur, for example, when the wheels of the rear axle lose traction, the device functions to automatically reengage the left-hand driven member with the driving member and positively drive the front axle from the engine until such time as the r ar wheels regain traction.

This result is brought about by the fact that, as soon as the speed of the left-hand driven member becomes less than that of the driving member 35, i. e., when the latter begins to move ahead of the former, the friction clutch efiect of the springs 59 again becomes operative to cause each holdout ring to move with its respective driven member since at that time there is no longer force opposing such movement other than the frictional contact between the end surfaces of the overlapped steps 62 of the holdout rings. in this connection, it will be understood that the friction springs 59 are so designed that the resistance offered thereby to slippage between the hold-out rings and the driven members is greater than the resistance to relative movement between the holdout rings oifered by the frictional contact between the end surfaces of the steps of lugs 58. As the driven member 36 and its holdout ring 38 drop rearwardly relative to the speeded-up driving member and driven member 37, the steps 62 of holdout ring 38 move back off the steps of holdout ring 39 until the beveled corners of the steps have cleared one another, at which time driven member 36 is free to return to the fully engaged position of Figs. 2 and 7 under the influence of spring ill as soon as its cam teeth 55 come opposite the spaces between the cam teeth of driven member 3?.

The driven clutch member 35 will then remain in fully engaged position and transmit driving torque to the front axle 2! as long as the wheels of rear axle 22 are slipping. But as soon as the rear wheels regain traction and again drive the vehicle, the left-hand driven member of the differential is again driven from the front axle at a greater velocity than the driving member 35 and is thereupon returned to and maintained in its normally disengaged position through the cooperative action of the cam teeth 5% and holdout rings 38 and 39 in the manner previously described.

Due to the symmetrical construction of the lugs of the holdout rings and the clearance provided between the side surfaces of the steps thereof when both sides of the differential are fully engaged, the mechanism functions in the same manner irrespective of the direction of rotation of the driving member, i. e., whether the vehicle is driving ahead or backing. It is also evident that, while one side of the differential may, and normally does, overrun the driving member, it cannot underrun the latter and thereby stall the vehicle in the event that the rear axle loses traction. In View of the fact that the holdout rings cooperate directly with one another and are rotatable with respect to the driven members, so that there is no positive operative connection between the driving member and the holdout rings, torque reversals which may occur while one side of the differential is overrunning do not effect reengagement of the overrunning driven member as is the case with the structures disclosed in the above mentioned Knoblock application. Serial No. 87,280. Consequently, the mechanism of the present invention is less subject to excessive stresses than these prior devices and is better suited for use as a transfer case differential.

Although there are certain advantages previously mentioned which inhere in the use of a symmetrically designed differential like that of Figs. 2-8, it may be desirable under some circumstances to reduce the number of parts by providing a device of unsymmetrical design such as that shown in Figs. 9-11 which represents a modified form of the invention.

As there illustrated, the mechanism comprises a casing 28, left-hand driving clutch and cam member 36 and associated holdout ring 33, spring ii! and spring retainer 42, shafts 33 and 3t and blocking ring 55, all of which are identical in structure with the corresponding elements of Figs. 2-8. The center drivin member 65 and right-hand driven member 55 are, however, of different form than the counterparts of the previously described embodiment, and the righthand holdout ring, compression spring and spring retainer of the latter have been omitted.

Referring particularly to Fig. 9, it will be seen that the left-hand side face of driving member 65 is provided with a set of clutch teeth 37 of the same construction, and which cooperate'with'the driven clutch teeth 45 of driven member 36 in the same manner, as the driving clutch teeth of the first embodiment. At the opposite side, instead of having a similar set of clutch teeth lying in a plane perpendicular to the axis of rotation of the differential, the driving member 65 has an annular, axially projecting portion 61 the inner surface of which is so machined as to provide a set of driving spline teeth 63 which extend parallel, rather than perpendicular, to the differential axis and are adapted to engage a set of similar driven spline teeth 69 formed on the outer circumferential surface of driven member 66. Although the driving and driven spline teeth 68 and 68 may be equal in number and spaced similarly to the driving and driven clutch teeth A! and 8 at the left-hand side of the differential, this is not essential to insure proper operation of the device irrespective of the direction of rotation of the driving member as long as the angular extent of the spaces between teeth 68 and 59 which constitute the backlash is the same as in the case of teeth 1;! and 48. The driven member 66 is splined to the shaft 34, and is positively prevented from outward axial movement relative to the driving member 65 by means of a blocking ring 55, just as in the device of Figs. 2-8, except that the blocking ring abuts directly against the wall of casing 28 instead of against the sprin retainer 43 which is omitted in the structure of Fig. 9.

The driven member 66 is provided with a cam ring portion '55 and cam teeth H of the same general character, and which cooperate with the cam portion 49 and teeth 53 of the left-hand driven member 35 in the same manner, as the corresponding parts of the previously described embodiment. The cam ring portion Hi and teeth 1' I, however, have a radial thickness greater than the cam ring 49 and teeth 50 of driven member 36 and extend radially outwardly beyond the latter into the same circumferential plane as that occupied by the radially inner portion of holdout ring 38.

The radially outer portion of cam ring is so machined as to form a plurality of circumferentially spaced spaces or recesses l2 equal in number to the stepped lugs 58 of holdout ring 38, the

end walls of said spaces being substantially co- 1 incident with the center planes of every fourth cam tooth ll; i. e., each space '12 has a circumferential extent sub tantially equal to that of three complete cam teeth. Inasmuch as the circumferential extent of each of the stepped lugs, measured bet een the side surfaces of the steps, is equal to approximately 2% times the circumferential extent of one full cam tooth, as previously described, the lugs may be received in the spaces with a total clearance between the side surfaces of the steps of each lug and the adjacent end walls of each space which is slightly less than the circumferential extent of one full cam tooth. The axial depth of each space or recess :2 is, as shown, sufficiently greater than the length of the central portion of each stepped lug that, when the lugs occupy their axially innermost positions in the spaces, there is a clearance between the ends of the lugs and the side walls of the spaces formed by the clutch tooth carrying portion of driven member 63.

It will also be seen from Fig. 10 that the axial dimensions of the stepped lugs are so proportioned that, when driven member 38 is fully ongaged with the driving member, the stepped por- 'tions of the lugs axially overlap the end walls engaged with the driving member as indicated in Fig. 9, the cam teeth 58 of said driven member are fully meshed with the teeth H of driven member 66 and the stepped lugs 53 of holdout ring 33 project their maximum distance into the spaces T2 in the cam ring portion ill of driven-member 86. Since at this time t ere is no force exerted on the holdout ring, other than inertia, tending to produce relative rotation between it and its associated driven member, the holdout ring rotates with driven member 36 without relative movement therebetween due to the friction clutch effect of spring 5: and floats, so to speak, in the spaces 72.

If, however, the left-hand side of the differential begins to overrun and the driven member 36 rotates at a greater velocity than the center driving member the cam teeth 58 of said driven member ride up on the cam teeth 'H of the right-hand driven member 56 and cause the overrunning driven member to move axially outwardly and disengage the left-hand set of clutch teeth 47 and 8. During the time that the cam teeth of driven member 35 are riding up the inclined sides of the teeth of member 66 and during the initial period of the ensuing end-to-end sliding contact of said teeth, the holdout ring 33 continues to move with the overrunning driven member 38 forwardly with respect to the driving member and driven member 65 to the frictional connection between the two elements established by the spring 59. As this forward movement continues, the advancing beveled corners 63 ofthe step 62 on holdout ring 38 come into contact with and slide over the corners of half-teeth l3 defining the end walls of spaces T2 and, spring 59 still being effective to resist relative rotation between holdout ring 38 and its associated driven member, move driven member 36 axially outwardly still further so as to completely separate the clutch and cam teeth of said member from the corresponding teeth of the driving member 65 and driven member 66. The for ward rotational movement of holdout ring 38 relative to driven member 66 then continues until the advancing side surfaces of the central portions of stepped lugs 58 of ring 38 come into abutment with the end walls of spaces l2, whereupon the holdout ring 38 becomes immobilized with respect to driven member 65 in the position shownin Fig. 11, with one step of each lug resting on the end of one of half-teeth '13. Thereafter holdout ring 38 slips frictionally with respect to driven member 38 as long as the latter rotates at a greater velocity than center driving member (55 and righthand driven member 25.

When the overrunning of the left-hand side of the difierential ceases, i. e., when the speed of rotation of the driving member 65 and driven member 66 increases until it reaches and then tends to exceed that of driven member 36, as would occur during slippage of the rear wheels of the vehicle of Fig. 1, the friction clutch efiect of spring 59 again becomes operative to cause holdout ring 38 to move with the associated driven member 36 since at that time there is no longer any force opposing such movement other than the frictional contact between the end surfaces of the steps 62 of the holdout ring and the ends of half-teeth '13 of driven member 86. As driven member and holdout ring 38 drop r arwardly relative to the driving member and driven member E6, the steps $2 or holdout ring 38 move back on" the half-teeth is until the beveled corners of the steps have cleared the corners of the end Walls of spaces ?2, at which time driven member 35 is free to return to the fully engaged position of Figs. 9 and 10 under the influence of spring 46 as soon as its cam teeth 56 come opposite the spaces between the cam teeth H of driven member $6.

The driven clutch member 3:6 will then remain in fully engaged position and transmit driving torque to the frontaxle 2! as long as the wheels of rear axle 22 are slipping. But as soon as the rear wheels regain traction and again drive the vehicle, the left-hand driven member of the differential is again driven from the front axle at a greater velocity than the driving member and is thereupon returned to and maintained its normally disengaged position through the cooperative action of the cam teeth as and H and holdout ring 38 in the manner previously described.

There is thus provided by the present invention an improved form of differential mechanism oi the overrunning clutch type characterized by the inclusion of novel means for maintaining one side of the mechanism in disengaged or declutched position as long as the driven member at the disengaged side overruns the driving member, which means are controlled by the relative velocities of said driven member and a cooper-ab ing member which is positively driven by the driving member at all times. The devices of the invention are particularly adapted for employment as transfer case differentials in motor vehicles wherein one axle or bogie is designed to normally overrun another axle or another bogie which is continuously driven from the engine, but the overrunning axle or bogie is also adapted to be positively driven when the wheels of the other lose traction; they may also be employed to advantage in installations where the front axle is also normally driven from the engine but must overrun when the vehicle makes a turn. Due to their novel construction, these mechanisms are dependable in operation, relatively economical to manufacture and service, and free from the defects of other devices heretofore proposed for the same general purposes.

While two specifically different differentials embodying the invention have been described and illustrated in the accompanying drawings, it will be obvious that the invention is not limited to the particular structures shown, but is capable of a variety of mechanical embodiments, and that various changes, which will now suggest themselves to those skilled in the art, may be made in the form, details in construction and arrangement of the parts without departing from the inventive concept. Reference is therefore to be had to the appended claims for a definition or" the limits of the invention.

What is claimed is:

1. in a transfer case differential for a pair of opposed axle driving shafts of the type embodying two sets of meshing driving and driven clutch elements, the combination of a cam member fixed to each of said driven clutch elements, said cam members having cam teeth cooperating with one another to disengage one set of driving and driven clutch elements by axial movement in one direction of the driven clutch e ement relative to the associated driving clutch element when the associated axle overruns the driving clutch element, a holdout ring carried by said axially movable driven clutch element which, upon overrunning, initially moves both axially and rotatably with said element relative to the associated driving clutch element and the other set of driving and driven clutch elements, sur- I aces on said ring which, during said initial movement, come into contact with cooperating surfaces on the other driven clutch element and prevent axial movement of said axially movable driven clutch element in the opposite direction to eifect reengagement with the driving clutch element, and means on said other driven clutch element operable when said surfaces come into contact for preventing further movement of said ring relative to said means as long as the overrunning continues, said ring being so mounted on said axially movable driven clutch element as to permit the latter to rotate relative to said ring as long as the latter is immobilized with respeot to said means.

2. A transfer case differential according to claim 1 including means for positively preventing disengagement of the other set of driving and driven clutch elements.

3. A transfer case differential according to claim 1 including a casing for said driving and driven clutch elements having a portion abutting said other driven clutch element and preventing disengagement thereof from the associated driving clutch element.

4. A differential mechanism of the class described comprising a driving member, a pair of driven members, cooperating clutch elements on said driving and driven members for transmitting torque from said driving member to said driven members, one of said driven members being axially movable relative to said driving member, cam means carried entirely by said driven members for causing the axial separation of said axially movable driven member and the driving member and disengagement of the cooperating clutch elements thereof when the velocity of said driven member exceeds that of said driving member, and a holdout ring rotatably mounted on said axially movable driven member for main taining said axial separation so long as the velocity of said driven member exceeds that of said driving member, the other driven member including means permitting a limited rotational movement of said holdout ring relative thereto but immobilizing said ring with respect thereto after said limited movement has taken place, whereupon the axially movable driven member rotates relative to said ring so long as the velocity of said member exceeds that of the driving member.

5. A difierential mechanism according to claim 4 wherein the holdout ring is provided with an axially projecting lug and the other driven memher is provided with a slot of greater circumferential extent than that of said lug into which said lug extends.

I 6. A differential mechanism according to claim 4 wherein the other driven member is immovable relative to said driving member so as to be positively driven by the latter at all times.

15 7. A differential mechanism of the class described comprising a driving member, a pair of driven members, cooperating clutch elements on said driving and driven members for transmitting torque from said driving member to said axially extending projections which, upon axial separation of said driving and driven members, come into abutment with cooperating portions of said other driven member and maintain said axial separation so long as the velocity of said one driven member exceeds that of said driving member, and means for frictionally clutching said holdout ring to said one driven member, said means normally resisting relative rotation between said ring and said driven member but yielding to permit such relative rotation when said one driven member is maintained in axially separated position by said ring.

8. A differential mechanism according to claim '7 wherein said holdout ring and the driven member on which it is mounted are so constructed as to provide an annular space therebetween, and which includes a friction spring housed in said space and frictionally engaging circumferentially spaced portions of both said ring and said driven member.

9. A differential mechanism according to claim 8 including a flange on said holdout ring engaging one side of said spring for preventing axial movement of said ring relative to the driven member on which it is mounted.

10. A transfer case differential mechanism comprising a driving member having clutch teeth formed on the opposite sides thereof, a pair of driven members having clutch teeth adaptedfor engagement with the clutch teeth of said driving member, one of said driven members being axially movable relative to the driving member so as to efiect disengagement of the clutch teeth thereof, cam means carried entirely by said driven members for disengaging said axially movable driven member from said driving member when said driven member rotates at a greater velocity than said driving member and the other driven member, a holdout ring rotatably mounted on each of said driven members, projections on each of said holdout rings extending toward the other ring, recesses in each of said holdout rings adapted to receive the projections of the other ring when both driven members are in engagement with the driving member, surfaces on said holdout rings adjacent said recesses which, when en- =gaged by said projections, hold the axially movable driven member out of engagement with the driving member, the projections of said holdout rings being moved into engagement with said surfaces when said axially movable driven member overruns and is disengaged from said driving member, and means forming part of said holdout rings for immobilizing said rings with respect to one another with the projections thereof in engagement with said surfaces as long as theoverrunning continues.

11. A transfercase differential mechanism ,ac-

cording to claim 10 including means for preventing disengagement of the other driven member from the driving member.

extending projections receivable 12. A transfer case difierential mechanism according to claim 10 including a casing for said driving and driven members having walls spaced from the outer edges of said driven members, and a blocking member interposed between the other driven member and the adjacent wall of said casing for preventing axial movement of said other driven member relative to the driving member.

13. In a differential mechanism of the type embodying a driving member having clutch teeth formed on the opposite sides thereof, a pair of driven members having clutch teeth engageable with those of said driving member and cam means carried entirely by said driven members for disengaging one of said driven members from the driving member when said driven member overruns the driving member, a pair of holdout rings mounted on said driven members adapted to manitain the overrunning member in disengaged position as long as the overrunning con.- tinues, one of said holdout rings having axially in recesses formed in the other holdout ring when both driven members are engaged with the driving member, axially raised surfaces on said other holdout ring adjacent said recesses against which .said projections abut when the overrunning driven member is disengaged from the driving member, and means forming a part of said other holdout ring for preventing rotation relative thereto of the first named holdout ring when said projections are in abutment with said axially raised surfaces as long as the overrunning continues.

14. A differential mechanism according to claim 13 wherein each of said holdout rings is rotatably mounted on, but incapable of axial movement relative to, the associated driven member, and is provided with a plurality of circumferentially spaced stepped lugs separated by recesses, the lugs of each ring extending into the recesses of the other when both driven members are engaged with the driving member and the steps of one ring abutting those of the other ring when the overrunning driven member is disengaged from the driving member.

15. In a differential mechanism of the type embodying-a driving member having clutch teeth formed on the opposite sides thereof, a pair of driven members having clutch teeth engageable with those of said driving member and cam means carried entirely by said driven members for disengaging one of said driven members from the driving member when said driven member overruns the driving member, a pair of holdout rings adapted to maintain the over-running driven member in disengaged position as long as the overrunning continues, said holdout rings being rotatably mounted on, but incapable of axial movement relative to, said driven members, an axially extending projection formed on one of said holdout rings, a recess in the other of said holdout rings into which said projection extends when both driven members are engaged with the driving member, and axially raised surfaces on each side of said projection and said recess adapted to abut one another and hold the overrunning driven member in disengaged position when relative rotation takes place between said driven members upon overrunning. said projection andrecess cooperating to prevent relative rotation between said holdout rings after said-axially raised surfaces have come into abutment as long as the overrunning continues. 16. A transfer case differential mechanism comprising a driving member having clutch teeth formed on the opposite sides thereof, a pair of driven members having clutch teeth engageable with those of said driving member, cam means carried entirely by said driven members for moving one of said driven members axially away from the driving member and disengaging the clutch teeth of said driven member from those of said driving member when said driven member overruns the driving member, a pair of holdout rings adapted to maintain the overrunning driven member in disengaged position as long as the overrunning continues, each of said holdout rings being rotatably mounted on one of said driven members and having a plurality of circumferentially spaced stepped lugs extending axially therefrom toward the other holdout ring, said lugs being separated by recesses into which the lugs of the other ring extend when both driven members are engaged with the driving member, the circumferential dimension of each of said lugs being less than that of the cooperating recess, and means frictionally clutching each holdout ring to the driven member on which it is mounted whereby the ring mounted on the overrunning driven member moves both axially and rotationally therewith when said driven member begins to overrun the driving member, the steps on said lugs being so formed that the initial axial and rotational movement of the holdout ring on said overrunning driven member brings said steps into abutment with the steps of the lugs of the other holdout ring and brings the central portions of said lugs into engagement with the portions of said other holdout ring defining the ends of said recesses, said frictional clutching means yielding to permit relative rotation between one of said holdout rings and the associated driven member when said lugs come into engagement with the ends of the recesses, whereby said lugs maintain the overrunning driven member in disengaged position as long as the overrunning continues.

17. A transfer case differential mechanism according to claim 16 wherein each of the driven members is provided with cam teeth cooperating with the cam teeth of the other driven member for initially disengaging the overrunning driven member from the driving member, and wherein the steps of said stepped lugs are slightly higher than said cam teeth.

18. A transfer case differential mechanism comprising an annular driving member, a pair of driven members located at the opposite sides of said driving member, cooperating clutch element on said driving and driven members for transmitting torque from said driving member to said driven members, one of said driven members being axially movable relative to said driving member, spring means urging said axially movable driven member toward said driving member to effect engagement of the cooperating clutch elements thereof, cam means for causing the axial separation of said axially movable driven member and the driving member and disengagement of the cooperating clutch elements thereof when the velocity of said driven member exceeds that of said driving member, said cam means comprising members fixed to said driven members extending axially toward one another through the central opening in said driving member and having cooperating cam elements at their adjacent inner edges, a holdout ring rotatably mounted on said axially movable driven member for maintaining said member axially separated from the driving member so long as the velocity of said driven member exceeds that of said driving member, said holdout ring also extending into the central opening in said driving member and having axially extending projections at the edge thereof adjacent the other driven member, and means carried by said other driven member providing surfaces against which said projections abut when the axially movable driven member is separated from said driving member.

19. A transfer case differential mechanism comprising an annular driving member, a pair of driven members located at the opposite sides of said driving member, cooperating clutch elements on said driving and driven members for transmitting torque from said driving member to said driven members, one of said driven members being axially movable relative to said driving member, spring means urging said axially movable driven member toward said driving member to eifect engagement of the cooperating clutch elements thereof, cam means for causing the axial separation of said axially movable driven member and the driving member and disengagement of the cooperating clutch elements thereof when the velocity of said driven member exceeds that of said driving member, said cam means comprising members fixed to said driven members extending axially toward one another through the central opening in said driving member and having cooperating cam elements at their adjacent inner edges, a holdout ring rotatably mounted on said axially movable driven member for maintaining said member axially separated from the driving member so long as the velocity of said driven member exceeds that of said driving member, said holdout ring also extending into the central opening in said driving member and having axially extending projections at the edge thereof adjacent the other driven member, and means carried by said other driven member providing recesses into which said projections extend when both driven members are fully engaged with the driving member and axially raised surfaces adjacent said recesses against which said projections abut when the axially movable driven member is separated from said driving member.

20. A transfer case differential mechanism comprising an annular driving member, a pair of driven members located at the opposite sides of said driving member, cooperating clutch element on said driving and driven members for transmitting torque from said driving member to said driven members, one of said driven members being axially movable relative to said driving member, spring means urging said axially movable driven member toward said driving member to effect engagement of the cooperating clutch elements thereof, cam means for causing the axial separation of said axially movable driven member and the driving member and disengagement of the cooperating clutch elements thereof when the velocity of said driven member exceeds that of said driving member, said cam means comprising members fixed to said driven members extending axially toward one another through the central opening in said driving member and having cooperating cam teeth at their adjacent inner edges, and a pair of holdout rings rotatably mounted on said driven members for maintaining said axially movable driven member axially separated from the driving member so long as the velocity of said driven mem- -ber exceeds that -of --sai'd "driving member, :said holdout rings also extending "into the central opening insaid driving member and having interengaging -projections and recesses at their -ad jacent inner edges, theprojections of each'ring extending-into the recesses of the other when both driven members are fully engaged-with the driving "member, axial separation of said axially movable driven member'from the driving member moving the projections of the associated holdout ring axially outwardly with respect to the recesses of theother ring and into abutment with the projections-0f the latter.

21. A transfer case differential mechanism according to claim 20 wherein the projections and recesses of each holdout ringare in the form of axially extending stepped lugs and'intervening spaces, respectively, the circumferential extent of-each space being g-reater than that of each lug to permita limited rotational movement of one 'holdout ring relative to the other when the ve- "locity of the axially movable driven member begins =-to change :1reiative to 'L-that nof dike-driving memberand :the other fdriven rmember.

'22. :A'transfer casevdifferential-mechanism accordingto claimi-2lzwherein theasteps of the lugs of thetwoholdoutringsraxiallyroverlapfora distance ;at least equal ito the'fheight of the cam teeth of "said driven members when both driven members arefullyengaged with the driving member.

IXLBERT F. MYERS.

References Qited ,in :the -file'of this :patent UNITED STATES' PA'IENTS 

